JP5595444B2 - DC-AC converter - Google Patents

Description

  The present invention relates to a converter, and more particularly to a DC-AC converter.

  In recent years, the main energy source of mankind has come from oil. The power or electricity required to move a car or power a thermal power plant is obtained by burning oil. However, the heat and exhaust gas generated by the burning of petroleum not only cause air pollution, but can worsen the global warming effect. In addition, oil production peaks within 10 years and then decreases year after year. This means that the price of oil (including electricity charges) is no longer cheap. Eventually, the energy crisis comes and will hit the world economy.

  In view of the above blow to the global economy, it has been sought to supply electricity or power to homes or offices efficiently and economically with renewable energy. So far, the development of renewable energy has become an important energy policy in developed countries as a win-win policy that balances power generation and environmental protection. Of various renewable energies (solar energy, wind energy, tidal energy, geothermal energy, biowaste energy), solar energy has become the mainstream. This is because solar energy generators have the advantages of environmental friendliness, ease of installation, maturity of commercialization, and overwhelming boost by the state. Therefore, solar energy has become a major option in developing distributed power supply systems in developed countries.

FIG. 1 shows a circuit of a conventional DC-AC converter. As shown in FIG. 1, a DC-AC converter 1 is used in a photovoltaic system connected to a solar grid, and thus the DC-AC converter 1 is also known as a photovoltaic inverter or a PV inverter. . The DC-AC converter 1 is configured in a non-isolated and full-bridge topology, and includes an input filter 10, a full-bridge switch circuit 11, and an output filter 12. Input filter 10 is composed of a first capacitor C _1, it receives a DC input voltage V _DC generated by solar cells, filtering the DC input voltage V _DC. The full bridge switch circuit 11 is connected to the output filter 12 and is composed of switch elements S ₁ -S _4. The first switch element S ₁ is connected in series with the second switch element S _2, and the third switch element S _3, 4 are connected switching element S ₄ in series, to form a full bridge circuit with two bridge arms. The switch elements S ₁ -S ₄ are controlled to be turned on / off by a control unit (not shown), so that the full bridge switch circuit 11 converts the filtered DC input voltage V _DC into the AC modulation voltage V _T. to enable. The output filter 12 is connected to the full bridge switch circuit 11 and includes a first inductor L ₁ , a second inductor L ₂ , and a second filtering capacitor C ₂ . The output filter 12 removes a high frequency component of the AC modulation voltage V _T, is used to output an AC output voltage V _o to the grid G.

In general, the switch elements S _{1 to} S ₄ of the full bridge switch circuit 11 are configured to operate by pulse width modulation (PWM). More precisely, the switch elements S ₁ -S ₄ of the full-bridge switch circuit 11 can operate under a bipolar switching mode or a unipolar switching mode according to the operation mode of the switch elements S ₁ -S ₄ . Referring to FIGS. 2 and 3, FIG. 2 is a waveform diagram of the modulation voltage of the full-bridge switch circuit of FIG. 1 operating under bipolar switching mode, and FIG. 3 operates under unipolar switching mode. FIG. 2 is a waveform diagram of a modulation voltage of the full bridge switch circuit of FIG. As shown in FIGS. 1 to 3, the switch elements S _{1 to} S ₄ are configured to operate at a high frequency under a bipolar switching mode. Under these conditions, AC modulation voltage V _T output by the full bridge switching circuit 11, as shown in FIG. 2, during the positive half cycle or negative half cycle, the positive DC input voltage V _DC and the negative Fluctuates between DC input voltage -V _DC . Under unipolar switching mode, only one bridge arm of the switch circuit operates at high frequency and the other bridge arm of the switch circuit is off during each half cycle. That is, this bridge arm is composed of the first switch element S ₁ and the second switch element S ₂ , and the other bridge arm is composed of the third switch element S ₃ and the fourth switch element S ₄ , alternately turned on and off, whereby, between 0 and a positive DC input voltage V _DC between AC modulation voltage V _T output by the full bridge switching circuit 11 as shown in FIG. 3 is a positive half-cycle Fluctuates and allows to vary between 0 and negative DC voltage -V _DC during the negative half cycle.

When the full-bridge switch circuit 11 is operating in the unipolar switching mode, only one bridge arm composed of two switch elements is configured to perform a high-frequency switching operation (on the other hand, bipolar switching) Under mode, the two bridge arms composed of the switch elements S ₁ -S ₄ perform high frequency switching operation.) At this time, the AC modulation voltage V _T varies between 0 and the positive DC input voltage V _DC , or varies between 0 and the negative DC input voltage −V _DC . Accordingly, the switching loss of the full bridge switch circuit 11 operating under the unipolar switching mode is smaller than the switching loss of the full bridge switch circuit 11 operating under the bipolar switching mode. In other words, the full bridge switch circuit 11 has better conversion efficiency under the unipolar switching mode. However, as shown in FIG. 1, since the parasitic capacitance C _p exists between the solar cell that generates the DC input voltage V _DC and the ground terminal, the full bridge switch circuit 11 operates under the unipolar switching mode. When the modulation voltage _VT has a high frequency component. Therefore, the relative voltage between the first output terminal A ′ and any node in the DC-AC converter 1 (eg, between the first output terminal A ′ and the common node N ′ (the node connected to the parasitic capacitance C _p )). Of the relative voltage between the second output terminal B ′ and the common node N ′ cannot be set to be maintained at a constant value at any time of switching. Thus, a large voltage variation occurs across the parasitic capacitance C _p, endangering users and devices. When the full bridge switch circuit 11 is operating in the bipolar switching mode, the leakage current can be avoided.

  Accordingly, Applicants have attempted to develop a DC-AC converter with better conversion efficiency and lower leakage current.

  An object of the present invention is to provide a DC-AC converter that addresses the problems of low conversion efficiency and high leakage current when the conventional DC-AC converter is applied to a solar power generation system connected to a solar grid. It is.

  To this end, the present invention includes a switch circuit configured to receive DC power, convert the DC power to an AC modulated voltage, and output between the first output terminal and the second output terminal. Provide DC-AC converter. The switch circuit includes a first switch branch including a first switch element and a second switch element connected in series with each other; a third switch element connected in parallel with the first switch branch and connected in series with each other; A second switch branch including a fourth switch element and a fifth switch element, wherein the first switch element and the second switch element are connected to the first output terminal, and the fourth switch element and the fifth switch element are Connected to the second output terminal. The DC-AC converter of the present invention has one end connected between the third switch element and the fourth switch element, and the other end connected between the first switch element and the second switch element and connected to the first output terminal. The sixth switch element is further included. The first switch element and the fifth switch element are turned on and off simultaneously and continuously, the sixth switch element is turned on during the positive half cycle, and the second switch element and the third switch element are turned on simultaneously. And it is continuously turned on and off, and the fourth switch element is turned on during the negative half cycle.

  The above and other features and advantages of the present invention will be better understood through the following detailed description and accompanying drawings.

FIG. 1 shows a circuit of a conventional DC-AC converter.

FIG. 2 is a waveform diagram of the modulation voltage of the full bridge switch circuit of FIG. 1 operating under the bipolar switching mode.

FIG. 3 is a waveform diagram of the modulation voltage of the full bridge switch circuit of FIG. 1 operating under the unipolar switching mode.

FIG. 4 shows a circuit of a DC-AC converter according to an embodiment of the present invention.

FIG. 5A shows a waveform diagram of control signals used in the circuit of FIG.

FIG. 5B shows a waveform diagram of the AC modulation voltage used in the circuit of FIG.

FIG. 6A shows a circuit of the control unit of FIG.

FIG. 6B shows a waveform diagram of control signals used in the circuit of FIG. 6A.

FIG. 7A shows a modified circuit of the control unit of FIG.

FIG. 7B shows a waveform diagram of control signals used in the circuit of FIG. 7A.

  Several exemplary embodiments embodying features and advantages of the invention are described in the following description paragraph. The present invention allows various modifications in various respects, and all do not depart from the scope of the present invention. The description and drawings herein are exemplary and should not be construed as limiting the invention.

FIG. 4 shows a circuit of a DC-AC converter according to an embodiment of the present invention. As shown in FIG. 4, the DC-AC converter 4 may be applied to a solar power generation system connected to a solar grid, and is a non-insulated circuit. DC-AC converter 4, DC device 8: receives DC input voltage V _DC from (eg solar cell), is used to convert the DC input voltage V _DC to the AC output voltage V _o. The AC output voltage V _o is supplied to an AC load 9 (eg, AC appliance or AC network system).

The DC-AC converter 4 includes an input filter 40, a switch circuit 41, an output filter 42, and a control unit 43. Input filter 40 is connected to each of the positive electrode and the negative electrode of the DC device 8 receives a DC input voltage V _DC, filters the DC input voltage V _DC. In this embodiment, the input filter 40, first may include a capacitor C _1.

Switch circuit 41 is connected to input filter 40 and includes switch elements S ₁ -S ₆ . The switch circuit 41 converts the filtered DC input voltage V _DC by the switching operation of the switch elements S _{1 to} S ₆ , and thereby converts the AC modulation voltage V _T between the first output terminal A and the second output terminal B. Used for output.

In this embodiment, the first switch element S ₁ and the second switch element S ₂ are connected in series with each other to form a first switch branch 411. One end of the first switch element S ₁ is connected to the positive electrode of the DC device 8 and the positive electrode of the input filter 40. One end of the second switch element S ₂ is connected to the negative electrode of the DC device 8 and the negative electrode of the input filter 40. The third switch element S ₃ , the fourth switch element S ₄ , and the fifth switch element S ₅ are connected in series with each other to form a second switch branch 412 connected in parallel with the first switch branch 411. One end of the third switch element S ₃ is connected to the positive electrode of the DC device 8 and the positive electrode of the input filter 40. One end of the fifth switching element S ₅ is connected to the negative electrode and the negative electrode of the input filter 40 of the DC device 8. One end of the sixth switch element S ₆ is connected between the third switch element S ₃ and the fourth switch element S ₄ of the second switch branch 412, and the other end of the sixth switch element S ₆ is the first output terminal. A is connected between the first switch element S ₁ and the second switch element S ₂ of the first switch branch 411.

In this embodiment, the switch elements S ₁ -S ₆ are constituted by MOSFETs having body diodes D ₁ -D ₆ as shown in FIG. The first body diode D ₁ and a second conduction direction of the body diode D ₂ is the direction from the second switching element S ₂ to the first switching element S _1. The conduction direction of the third body diode D ₃ , the fourth body diode D ₄ , and the fifth diode D _{5 is} the direction from the fifth switch element S ₅ to the third switch element S ₃ . The conduction direction of the sixth body diode D _{6 is} the direction from the first switch branch 411 to the second switch branch 412.

The control unit 43 is connected to the control terminals of the switch elements S ₁ -S ₆ . The control unit 43 generates a PWM-based control signal V _c1 -V _c6 and is used to control on / off of the switch elements S ₁ -S ₆ .

The output filter 42 is connected to the first output terminal A and the second output terminal B of the switch circuit 41. Further, the output filter 42 is connected to a load 9, receives the AC modulation voltage V _T, removes high-frequency components of the AC modulation voltage V _T, thereby outputting an AC output voltage V _o to the AC load 9. In this embodiment, the output filter 42 includes a first inductor L ₁ , a second inductor L ₂ , and a second capacitor C ₂ . One end of the first inductor L ₁ is connected to the first output terminal A. One end of the second inductor L ₂ is connected to the second output terminal B. The second capacitor C ₂ is connected to the first inductor L ₁ , the second inductor L ₂ , and the AC load 9.

Next, the operation of the DC-AC converter 4 of the present invention will be described. Referring to FIGS. 5A and 5B and FIG. 4, FIG. 5A shows a waveform diagram of a control signal used in the circuit of FIG. 4, and FIG. 5B shows a waveform of an AC modulation voltage used in the circuit of FIG. The figure is shown. As shown in FIGS. 4, 5A and 5B, during the positive half cycle (eg, between point 0 and the first point T ₁ ), the first control signal V _c1 and the fifth control signal V _c5 are PWM It fluctuates with. That is, the first control signal V _c1 and the fifth control signal V _c5 are alternately switched between a disabled state and an enabled state. Thus, the first switching element S ₁ and the fifth switching element S ₅ is simultaneously and continuously on and off. Further, the second control signal V _c2 , the third control signal V _c3 , and the fourth control signal V _c4 remain in an invalid state. Accordingly, the second switch element S ₂ , the third switch element S ₃ , and the fourth switch element S ₄ are turned off. Further, the sixth control signal V _c6 remains in the valid state, and therefore the sixth switch element S ₆ is turned on.

Therefore, when both the first switch element S ₁ and the fifth switch element S ₅ are turned on during the positive half cycle, the current output by the DC device 8 is the first switch element S ₁ and the first inductor L. ₁ flows in this order through the second capacitor C ₂ , the second inductor L ₂ , and the fifth switch element S ₅ . Therefore, the DC power output by the DC device 8 is filtered and converted to AC power, and supplied to the AC load 9. On the other hand, the first inductor L ₁ and the second inductor L ₂ store energy. When both the first switch element S ₁ and the fifth switch element S ₅ are turned off during the positive half cycle, the energy stored in the first inductor L ₁ and the second inductor L ₂ is turned off. 4 flows through the sixth switching element S ₆ that is a fourth body diode D ₄ and on the switching element S _4. Accordingly, the AC load 9 continuously receives the energy output by the DC device 8.

During the negative half cycle (eg, between the first point T ₁ and the second point T ₂ ), the second control signal V _c2 and the third control signal V _c3 fluctuate with PWM. That is, the second control signal V _c2 and the third control signal V _c3 are alternately switched between the invalid state and the valid state. Accordingly, the second switching element S ₂ and the third switch element S ₃ are simultaneously and continuously on and off. Furthermore, the first control signal V _c1 , the fifth control signal V _c5 , and the sixth control signal V _c6 transition to an invalid state. Accordingly, the first switch element S ₁ , the fifth switch element S ₅ , and the sixth switch element S ₆ are turned off. Furthermore, the fourth control signal V _c4 transitions to the valid state. Accordingly, the fourth switching element S ₄ is turned on.

Therefore, when both of the second switching element S ₂ and the third switch element S ₃ is turned on during the negative half-cycle, the current output by the DC device 8, the third switching element S _3, a fourth switching element It flows in this order through S ₄ , second inductor L ₂ , second capacitor C ₂ , first inductor L ₁ , and second switch element S ₂ . Accordingly, the DC power output by the DC device 8 is filtered and converted into AC power, and supplied to the AC load 9. On the other hand, the first inductor L ₁ and the second inductor L ₂ store energy. When both the second switch element S ₂ and the third switch element S ₃ are turned off during the negative half cycle, the energy stored in the first inductor L ₁ and the second inductor L ₂ is turned off. It flows through the fourth switching element S ₄ that is a sixth body diode D ₆ and on the sixth switching element S _6. Accordingly, the AC load 9 continuously receives the energy output by the DC device 8.

Referring to FIG. 5B, when the fourth switch element S ₄ and the sixth switch element S ₆ are arranged, the AC modulation voltage V _T output by the switch circuit 41 is a positive predetermined value between 0 and a positive half cycle. It fluctuates between values V _r and fluctuates between 0 and a negative predetermined value −V _r during the negative half cycle. Therefore, the actual operation of the switch circuit 41 is similar to the operation of the full bridge switch circuit 11 operating under the unipolar switching mode of FIG. Therefore, the DC-AC converter 4 of the present invention can reduce the switching loss of the internal switch element of the switch circuit 41 and increase the conversion efficiency. Also, the relative voltage between the first output terminal A and a predetermined node in the DC-AC converter, and the relative voltage between the second output terminal B and a predetermined node in the DC-AC converter (example: FIG. 4). The first relative voltage V _AN between the first output terminal A and the node N (the node connected to the parasitic capacitance C _p ) and the second relative voltage V _BN between the second output terminal B and the node N shown in FIG. At any point in time, the arithmetic average value (total average) is set to be maintained at a constant value. Therefore, the parasitic capacitance C _p does not induce a large voltage change. In this way, the occurrence of leakage current will be suppressed and the risk to the user and the device will be reduced.

In the above embodiment, the first control signal V _c1 , the second control signal V _c2 , the third control signal V _c3 , and the fifth control signal V _c5 are high-frequency PWM signals, and the fourth control signal V _c4 and the second control signal V _c4 The 6 control signal V _c6 is a low frequency PWM signal.

Next, the circuit of the control unit 43 in FIG. 4 will be described. Referring to FIGS. 6A and 6B, FIG. 6A shows a circuit of the control unit of FIG. 4, and FIG. 6B shows a waveform diagram of control signals used in the circuit of FIG. 6A. The control unit 43 includes a first comparator 430, a second comparator 431, a third comparator 432, and a NOT gate 433. Positive input terminal of the first comparator 430 is used to receive the first sine-wave signal V _1, the negative input terminal of the first comparator 430 is grounded. The output terminal of the first comparator 430 is connected to the control terminal of the sixth switch element S _6, and outputs a sixth control signal V _c6. Positive input terminal of the second comparator 431 is used to receive the first sine-wave signal V _1, the negative input terminal of the second comparator 431 is used to receive the triangular signal V _TRI. The output terminal of the second comparator 431 is connected to the control terminal of the first switch element S _{1 and} the control terminal of the fifth switch element S ₅ to output the first control signal V _c1 and the fifth control signal V _c5. used. The positive input terminal of the third comparator 432 is used to receive a second sine wave signal V ₂ having a phase difference of 180 degrees with respect to the first sine wave signal V ₁ . The negative input terminal of the third comparator 432 is used to receive the triangular signal _VTRI . The output terminal of the third comparator 432 is connected to the control terminal of the second switch element S _{2 and} the control terminal of the third switch element S ₃ to output the second control signal V _c2 and the third control signal V _c3. used. Input terminal of the NOT gate 433 is connected to the output terminal of the first comparator 430, the output terminal of the NOT gate 433 is connected to the control terminal of the fourth switching element S _4. The NOT gate 433 is used to invert the sixth control signal V _c6 and thereby output the fourth control signal V _c4 .

It goes without saying that the circuit of the control unit 43 is not limited to the exact form described here. Referring to FIGS. 7A and 7B, FIG. 7A shows a circuit after the change of the control unit 43, and FIG. 7B shows a waveform diagram of control signals used in the circuit of FIG. 7A. In FIG. 7A, the control unit 43 includes a first comparator 730, a second comparator 731, a third comparator 732, a NOT gate 733, a first AND gate 734, a second AND gate 735, and a rectifier 736. Rectifier 736 receives the sine wave signal V _3, is used to a sine wave signal V ₄ which is rectified by rectifying a sinusoidal signal V _3.

Positive input terminal of the first comparator 730 is connected to the rectifier 736 is used to receive the sine wave signal V ₄ which rectified. The negative electrode of the first comparator 730 is used to receive the triangular signal V _TRI . The output terminal of the first comparator 730 is connected to the first input terminal of the first AND gate 734. The positive input terminal of the second comparator 731 is used to receive the sine wave signal V ₃ . The negative input terminal of the second comparator 731 is grounded. The output terminal of the second comparator 731 is connected to the control terminal of the sixth switch element S _6, it is used to output a sixth control signal V _c6. The positive input terminal of the third comparator 732 is connected to the rectifier 736 and is used to receive the rectified sine wave signal V ₄ . The negative electrode of the third comparator 732 is used to receive the triangular signal _VTRI . The output terminal of the third comparator 732 is connected to the first input terminal of the second AND gate 735.

The input terminal of the NOT gate 733 is connected to the output terminal of the second comparator 731 and is used to receive the sixth control signal V _c6 . Output terminal of the NOT gate 733 is connected to the fourth switching element S _4. The NOT gate 733 is used to invert the sixth control signal V _c6 and thereby output the fourth control signal V _c4 to the output terminal of the NOT gate 733. The second input terminal of the first AND gate 734 is connected to the output terminal of the second comparator 731 and is used to receive the sixth control signal V _c6 . The output terminal of the 1AND gate 734 is connected to the control terminal of the first switching element S ₁ and the control terminal of the fifth switch element S _5, to output a first control signal V _c1 and the fifth control signal V _c5 used. The second input terminal of the second AND gate 735 is connected to the output terminal of the NOT gate 733 and is used to receive the fourth control signal V _c4 . The output terminal of the second AND gate 735 is connected to the control terminal of the second switch element S _{2 and} the control terminal of the third switch element S ₃ to output the second control signal V _c2 and the third control signal V _c3. used.

  In summary, the DC-AC converter of the present invention is configured to reduce the switching loss of the internal switch elements of the mounted switch circuit by arranging the fourth switch element and the sixth switch element. Therefore, the conversion efficiency of the DC-AC converter is improved. Also, DC devices do not induce large voltage changes across the parasitic capacitance. Therefore, the leakage current can be suppressed, and the risk to the user and the device can be reduced.

  Although the present invention has been described with respect to what is presently considered to be the most practical and preferred embodiments, it should be understood that the invention need not be limited to the disclosed embodiments. . On the contrary, the invention is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims. The appended claims are accorded the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustrations should not be taken as limiting the scope of the invention which is defined by the appended claims.

Claims (14)

The switch circuit is configured to receive DC power, convert the DC power into an AC modulation voltage, and output the DC power between the first output terminal and the second output terminal.
A first switch branch including a first switch element and a second switch element connected in series with each other;
A second switch branch including a third switch element, a fourth switch element, and a fifth switch element connected in parallel with the first switch branch and connected in series with each other;
A sixth switch element having one end connected between the third switch element and the fourth switch element and the other end connected between the first switch element and the second switch element and connected to the first output terminal; ,
The first switch element and the second switch element are connected to the first output terminal, the fourth switch element and the fifth switch element are connected to the second output terminal, and the first switch element and the fifth switch element are simultaneously and The sixth switch element is turned on / off continuously, and the sixth switch element is turned on during the positive half cycle. The second switch element and the third switch element are turned on / off simultaneously and continuously, and the fourth switch element is turned on / off. Is a DC-AC converter that turns on during the negative half cycle. 2. The DC-AC converter according to claim 1, wherein the second switch element, the third switch element, and the fourth switch element are turned off during the positive half cycle, and the first switch element, the first switch element, The 5 switch element and the 6th switch element are DC-AC converters that are off during the negative half cycle. 3. The DC-AC converter according to claim 2, wherein the DC-AC converter is connected to the first switch element, the second switch element, the third switch element, the fourth switch element, the fifth switch element, and the sixth switch element. A DC-AC converter further comprising a control unit that controls a switching operation of the switch element, the second switch element, the third switch element, the fourth switch element, the fifth switch element, and the sixth switch element. 4. The DC-AC converter according to claim 3, wherein the control unit is
A first comparator having a positive input terminal for receiving the first sine wave signal, a negative input terminal connected to the ground terminal, and an output terminal connected to the control terminal of the sixth switch element;
A second comparator having a positive input terminal for receiving the first sine wave signal, a negative input terminal for receiving the triangular signal, and an output terminal connected to the control terminal of the first switch element and the control terminal of the fifth switch element;
A third comparator having a positive input terminal for receiving the second sine wave signal, a negative input terminal for receiving the triangular signal, and an output terminal connected to the control terminal of the second switch element and the control terminal of the third switch element;
A DC-AC converter comprising a NOT gate having an input terminal connected to the output terminal of the first comparator and an output terminal connected to the control terminal of the fourth switch element. 5. The DC-AC converter according to claim 4, wherein the first sine wave signal has a phase difference of 180 degrees with respect to the second sine wave signal. 4. The DC-AC converter according to claim 3, wherein the control unit is
A rectifier that receives a sine wave signal and rectifies the sine wave signal into a rectified sine wave signal;
A first comparator having a positive input terminal connected to the rectifier and a negative input terminal for receiving a triangular signal;
A second comparator having a positive input terminal for receiving the sine wave signal, a negative input terminal connected to the ground terminal, and an output terminal connected to the control terminal of the sixth switch element;
A third comparator having a positive input terminal connected to the rectifier and a negative input terminal for receiving a triangular signal;
A NOT gate having an input terminal connected to the output terminal of the second comparator and an output terminal connected to the control terminal of the fourth switch element;
The first input terminal connected to the output terminal of the first comparator, the second input terminal connected to the output terminal of the second comparator, and the control terminal of the first switch element and the control terminal of the fifth switch element A first AND gate having an output terminal;
A first input terminal connected to the output terminal of the NOT gate, a second input terminal connected to the output terminal of the third comparator, and an output connected to the control terminal of the second switch element and the control terminal of the third switch element A DC-AC converter comprising a second AND gate having a terminal. 2. The DC-AC converter according to claim 1, wherein the first switch element, the second switch element, the third switch element, the fourth switch element, the fifth switch element, and the sixth switch element are in a pulse width modulation mode. A DC-AC converter that is configured to operate below. 2. The DC-AC converter according to claim 1, wherein the first switch element, the second switch element, the third switch element, and the fifth switch element are configured to be turned on and off at a high frequency. The 4 switch element and the 6th switch element are DC-AC converters configured to be turned on and off at a low frequency. 2. The DC-AC converter according to claim 1, wherein the DC-AC converter is a non-insulated DC-AC converter. 2. The DC-AC converter according to claim 1, wherein the DC-AC converter suppresses a voltage change across a parasitic capacitance in a solar cell when applied to a solar power generation system connected to a solar grid. , DC-AC converter. 2. The DC-AC converter according to claim 1, wherein the first switch element, the second switch element, the third switch element, the fourth switch element, the fifth switch element, and the sixth switch element are metal oxide semiconductors. DC-AC converter composed of field effect transistors. 12. The DC-AC converter according to claim 11, wherein each of the first switch element, the second switch element, the third switch element, the fourth switch element, the fifth switch element, and the sixth switch element is a body diode. The conduction direction of the body diode of the first switch element and the body diode of the second switch element is the direction from the second switch element to the first switch element, and the body diode and the fourth switch element of the third switch element The conduction direction of the body diodes of the body switch and the fifth switch element is the direction from the fifth switch element to the third switch element, and the conduction direction of the body diode of the sixth switch element is the second direction from the first switch branch. DC-AC converter, which is the direction to the switch branch. 2. The DC-AC converter according to claim 1, wherein the DC-AC converter is connected to the switch circuit, receives a DC input voltage, filters the DC input voltage, and outputs the filtered DC input voltage to the switch circuit for conversion. DC-AC converter, further equipped with an input filter. 2. The DC-AC converter according to claim 1, further comprising an output filter connected to the switch circuit to remove a high-frequency component of the AC modulation voltage and thereby output an AC output voltage. 3. .